This thesis primarily addresses the systematic modification of polyamides, poly(amide- imide)s, polyimides and polyurethanes to yield high performance poly(thiourea-amide)s, poly(thiourea-amide-imide)s, imide)s, poly(thiourea-ether-imide)s, poly(urethane-thiourea)s, poly(phenylthiourea-azomethine- poly(urethane-thiourea-imide)s and poly(urethane- azomethine-thiourea)s. The foremost goal of current research is the structural modification of polymers exploiting the synthetic chemistry to attain excellent solubility via slightly disrupting polymer chain regularity and packing. Various synthetic schemes were developed for the inclusion of thiourea moieties along with other desired linkages in these polymers. The designed monomers (dinitro, diamines, dicarboxylic acids, diacid chlorides, diols and diisocyanates) bearing pre-formed linkages were then synthesized and employed for the preparation of novel thiourea-based polymeric materials. The incorporation of different functional groups provides an opportunity to control certain physical properties such as solvent miscibility, η inh , crystallinity, molecular weight, thermal stability and flame retardancy of the resulting polymers. The effect of thiourea and other functional groups on the properties of newly synthesized polymers were scrutinized together with their structure-property relationship. Major tools utilized for the examination of polymer properties are FTIR, 1 H NMR, solubility, viscometry, GPC, TGA, DSC and XRD. Novel thiourea-based polymers demonstrated outstanding thermal stability without deteriorating their organosolubility or processability. Another objective of the work was to evaluate the expedient applications and potential relevance of these valuable high-performance materials for advanced technologies. The processable poly(thiourea-amide)s, poly(thiourea- amide-imide)s, poly(thiourea-ether-imide)s and poly(urethane-azomethine-thiourea)s were found to have superior thermal stability as well as non-flammability. Poly(phenylthiourea-azomethine- imide)s having C=S and –C=N– moieties can act as imminent contenders to fabricate certain electrically conducting materials. Poly(thiourea-amide)s, in addition to the excellent solubility and thermal resistance, can be employed as solid extracting phases for the elimination of environmentally toxic metal ions from aqueous media. Prior to this effort, reported in peer- reviewed journals, synthesis of high temperature polymers bearing C=S entity was an unexplored area. Easy processability, high molar mass, heat and flame stability, electrical conductivity, etc, depict their high adaptability in future, rendering them backbone materials in polymer science.